1. Field of the Invention
The present invention relates to endoscopes and, more particularly, to endoscopes manufacturable sufficiently inexpensively to be disposable after single patient use, while being at least equal in optical performance to conventional endoscopes requiring sterilization.
2. Description of the Prior Art
Endoscopic or least invasive surgery has many advantages over conventional "open" surgery. Patients who have undergone endoscopic surgery rather than open surgery experience vastly less trauma and much faster recoveries, leading to improvement in the quality of health care together with reduction in the cost of health care. These advantages have spurred extensive development of endoscopes.
The term "endoscope" as used herein refers to an elongated optical probe capable of presenting a visible image of the interior of a body cavity, joint, organ or the like to a physician on either an eyepiece or a video screen. The endoscope is typically introduced into the body cavity through a bore in another device (also typically referred to in the art as an endoscope, or as an endoscope sheath) including a light source as well as other bores for introducing surgical instruments, water, air, suction and the like. Endoscopes as optimized for various surgical procedures are referred to as arthroscopes, cystoscopes, proctoscopes, laparoscopes and the like.
The art has for some years sought to develop a suitable disposable endoscope. The surgical requirement of absolute sterility is difficult to satisfy with conventional endoscopes as these complex instruments are not readily amenable to conventional sterilization techniques. The spread of infectious disease is of particular concern and requires that care and caution be employed during the sterilization process. Accordingly, there is a strong need for a suitable disposable endoscope, that is, one made sufficiently inexpensively as to be cost-effective for disposal after single-patient use.
Endoscopes typically consist of a distal objective for forming an optical image of the interior of the body cavity, bone, joint or organ, a transfer module (sometimes termed a "relay section") for transmitting the image from the distal end of the probe to its proximal end, and an ocular at the proximal end of the transfer module for presenting the image to an eyepiece, a video camera or the like. Typically, the ocular will contain the movable focusing components of the endoscope.
One of the difficult tasks in designing a satisfactory endoscope is that of designing the transfer module. The transfer module must be capable of transmitting the image formed by the objective to the ocular without significant loss of brightness or sharpness in the image. Early designs included numerous glass refractive elements, each requiring extensive polishing. The high cost of manufacture precluded use of these designs for disposable endoscopes.
More recently it has been suggested that the refractive optical elements of the transfer module should be molded of plastic, while the transmitting elements could be formed of much less expensive plano glass rods, i.e. glass rods having flat ends. Indeed, provision of the curved surfaces in optical systems by employment of molded plastic members, and using glass only for flat surfaced elements, is suggested by optical design textbooks; see, e.g., The Handbook of Plastic Optics, 2nd edition, published by U.S. Precision Lens, Inc. (1983), at page 86. However, despite this suggestion, there is no prior art disclosure or teaching of an endoscope providing adequate optical performance capable of manufacture at sufficiently low cost to be disposable.
Prior art endoscopes have typically been designed such that the objective provides a self-corrected image to the transfer module, the image then being transmitted with as little further aberration as possible to an ocular group. It is also known to employ the transfer module to correct aberration introduced by the objective. In either case the image presented by the probe to the objective is fully corrected. Typically the ocular designs employed have included two doublets placed back to back; this form permits separating the doublets at an afocal space. The first doublet is employed as a simple magnifier of the image, and the second doublet as a focusing element to allow a video camera to form the visible image on a display screen. However, this essentially simplified ocular design requires the image formed by the combination of the objective and the transfer module to be self-corrected. The cost of manufacture of suitable objective and transfer module components is too great for single patient disposable use.
Prior endoscopes have commonly also employed a fore-oblique prism in the tip of the endoscope to provide an off-axis field of view, that is, centered about an axis at an angle to the optical axis of the probe, so that by rotating the probe the surgeon has an effectively wider field of view than otherwise possible. In the prior art, such fore-oblique prisms have been manufactured by separately manufacturing two or three prisms of glass of high refractive index, separately coating the appropriate surfaces with reflective material, bonding the prisms together in an assembly jig requiring very high precision, and finally grinding the outer surface of the assembly to the desired cylindrical form. These manufacturing steps are very labor intensive and time-consuming, and render such fore-oblique prisms in the prior art much too expensive for use in a disposable device for single patient usage.
Another constraint on endoscope design arises because from time to time during surgery the surgeon may wish to change the endoscope's viewing angle, that is, to vary the angle between the center of the field of view and the optical axis of the probe. While endoscope designs have been proposed permitting variation of the viewing angle by moving a pivoted mirror or the like at the distal tip of the endoscope, these designs have been highly impractical. Variation of the viewing angle is possible in practical endoscopes only by removing a first probe from the surgical portal and substituting a second probe having a different viewing angle. To do so employing conventional re-usable endoscopes requires sterilization of several different endoscopes at substantial cost. If a video camera were being used to display the image, as is typical, this procedure would normally also necessitate disconnecting the ocular of the first endoscope from the video camera and reconnecting a second endoscope. It would be desirable to provide disposable endoscope probes having differing viewing angles all mating with the same nondisposable ocular, so that the probe could be replaced conveniently and discarded at reasonable cost if the surgeon desired to change viewing angles.
Endoscopic objectives found in the prior art have required glass elements of very high refractive index and having large differences in their spectral dispersion to provide control of optical aberration. These prior art designs have been limited to all-spherical surface design forms because of the cost of producing aspheric surfaces in glass. More specifically, one prior art endoscope objective design form uses a piano-concave flint glass element of very high refractive index preceding the prism element, a high index of refraction convex crown glass element bonded to the preceding prism element, a high index of refraction biconvex crown glass element, and a doublet including one element each of crown and flint glass. In the prior art, the high cost of production of these elements, having optical surfaces sufficiently steep to require individual polishing, had precluded use of this design for a disposable endoscope.
Until the present invention, there has been provided no design for an endoscope including a disposable probe that provides satisfactory optical performance, including convenient variation of viewing angle, while being manufacturable sufficiently inexpensively to be cost-effective for single-patient disposable use.